This invention relates to a plate clamping device for mounting a printing plate on a plate cylinder of a web-fed rotary printing press.
In a conventional web-fed rotary printing press, a printing plate wrapped about a plate cylinder is mounted under tension on the plate cylinder by clamping the opposite ends of the printing plate between the inner walls of an axial slot formed on the periphery of the plate cylinder and a plate clamping shaft disposed in the slot and then rotating the plate clamping shaft. After clamping, the printing plate should be uniformly tensioned in all directions, and the clamp should not be loosened to release the printing plate for preventing register errors during printing.
In a conventional plate clamping device, an eccentric plate clamping shaft is journalled by bearers at both longitudinal ends of the plate cylinder, and the opposite ends of the printing plate are inserted into gaps between the plate clamping shaft and the inner walls of the slot so as to clamp the printing plate by the wedge action of the plate clamping shaft caused by the tension of the printing plate. As a consequence, the long plate clamping shaft journalled at its opposite ends has a tendency to be bent by the tension of the printing plate so that the printing plate is not wrapped under uniform tension. Where the thickness of the printing plate is small, sufficient clamping force can not be provided, whereas where the thickness of the printing plate is large, insertion of both ends thereof into the gaps becomes difficult. Accordingly, it is difficult to set the gaps for any thickness of the printing plate. In other words the range of the thickness of the printing plate is limited.